content: // Protocol Buffers - Google's data interchange format
  // Copyright 2008 Google Inc.  All rights reserved.
  // https://developers.google.com/protocol-buffers/
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  package com.google.protobuf;
  
  import com.google.protobuf.Descriptors.Descriptor;
  import com.google.protobuf.Descriptors.FieldDescriptor;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Map;
  import java.util.Set;
  
  /**
   * A table of known extensions, searchable by name or field number.  When
   * parsing a protocol message that might have extensions, you must provide
   * an {@code ExtensionRegistry} in which you have registered any extensions
   * that you want to be able to parse.  Otherwise, those extensions will just
   * be treated like unknown fields.
   *
   * <p>For example, if you had the {@code .proto} file:
   *
   * <pre>
   * option java_class = "MyProto";
   *
   * message Foo {
   *   extensions 1000 to max;
   * }
   *
   * extend Foo {
   *   optional int32 bar;
   * }
   * </pre>
   *
   * Then you might write code like:
   *
   * <pre>
   * ExtensionRegistry registry = ExtensionRegistry.newInstance();
   * registry.add(MyProto.bar);
   * MyProto.Foo message = MyProto.Foo.parseFrom(input, registry);
   * </pre>
   *
   * <p>Background:
   *
   * <p>You might wonder why this is necessary.  Two alternatives might come to
   * mind.  First, you might imagine a system where generated extensions are
   * automatically registered when their containing classes are loaded.  This
   * is a popular technique, but is bad design; among other things, it creates a
   * situation where behavior can change depending on what classes happen to be
   * loaded.  It also introduces a security vulnerability, because an
   * unprivileged class could cause its code to be called unexpectedly from a
   * privileged class by registering itself as an extension of the right type.
   *
   * <p>Another option you might consider is lazy parsing: do not parse an
   * extension until it is first requested, at which point the caller must
   * provide a type to use.  This introduces a different set of problems.  First,
   * it would require a mutex lock any time an extension was accessed, which
   * would be slow.  Second, corrupt data would not be detected until first
   * access, at which point it would be much harder to deal with it.  Third, it
   * could violate the expectation that message objects are immutable, since the
   * type provided could be any arbitrary message class.  An unprivileged user
   * could take advantage of this to inject a mutable object into a message
   * belonging to privileged code and create mischief.
   *
   * @author kenton@google.com Kenton Varda
   */
  public class ExtensionRegistry extends ExtensionRegistryLite {
    /** Construct a new, empty instance. */
    public static ExtensionRegistry newInstance() {
      return new ExtensionRegistry();
    }
  
    /** Get the unmodifiable singleton empty instance. */
    public static ExtensionRegistry getEmptyRegistry() {
      return EMPTY_REGISTRY;
    }
  
  
    /** Returns an unmodifiable view of the registry. */
    @Override
    public ExtensionRegistry getUnmodifiable() {
      return new ExtensionRegistry(this);
    }
  
    /** A (Descriptor, Message) pair, returned by lookup methods. */
    public static final class ExtensionInfo {
      /** The extension's descriptor. */
      public final FieldDescriptor descriptor;
  
      /**
       * A default instance of the extension's type, if it has a message type.
       * Otherwise, {@code null}.
       */
      public final Message defaultInstance;
  
      private ExtensionInfo(final FieldDescriptor descriptor) {
        this.descriptor = descriptor;
        defaultInstance = null;
      }
      private ExtensionInfo(final FieldDescriptor descriptor,
                            final Message defaultInstance) {
        this.descriptor = descriptor;
        this.defaultInstance = defaultInstance;
      }
    }
  
    /**
     * Deprecated. Use {@link #findImmutableExtensionByName(String)} instead.
     */
    public ExtensionInfo findExtensionByName(final String fullName) {
      return findImmutableExtensionByName(fullName);
    }
  
    /**
     * Find an extension for immutable APIs by fully-qualified field name,
     * in the proto namespace. i.e. {@code result.descriptor.fullName()} will
     * match {@code fullName} if a match is found.
     *
     * @return Information about the extension if found, or {@code null}
     *         otherwise.
     */
    public ExtensionInfo findImmutableExtensionByName(final String fullName) {
      return immutableExtensionsByName.get(fullName);
    }
  
    /**
     * Find an extension for mutable APIs by fully-qualified field name,
     * in the proto namespace. i.e. {@code result.descriptor.fullName()} will
     * match {@code fullName} if a match is found.
     *
     * @return Information about the extension if found, or {@code null}
     *         otherwise.
     */
    public ExtensionInfo findMutableExtensionByName(final String fullName) {
      return mutableExtensionsByName.get(fullName);
    }
  
    /**
     * Deprecated. Use {@link #findImmutableExtensionByNumber(
     * Descriptors.Descriptor, int)}
     */
    public ExtensionInfo findExtensionByNumber(
        final Descriptor containingType, final int fieldNumber) {
      return findImmutableExtensionByNumber(containingType, fieldNumber);
    }
  
    /**
     * Find an extension by containing type and field number for immutable APIs.
     *
     * @return Information about the extension if found, or {@code null}
     *         otherwise.
     */
    public ExtensionInfo findImmutableExtensionByNumber(
        final Descriptor containingType, final int fieldNumber) {
      return immutableExtensionsByNumber.get(
        new DescriptorIntPair(containingType, fieldNumber));
    }
  
    /**
     * Find an extension by containing type and field number for mutable APIs.
     *
     * @return Information about the extension if found, or {@code null}
     *         otherwise.
     */
    public ExtensionInfo findMutableExtensionByNumber(
        final Descriptor containingType, final int fieldNumber) {
      return mutableExtensionsByNumber.get(
          new DescriptorIntPair(containingType, fieldNumber));
    }
  
    /**
     * Find all extensions for mutable APIs by fully-qualified name of
     * extended class. Note that this method is more computationally expensive
     * than getting a single extension by name or number.
     *
     * @return Information about the extensions found, or {@code null} if there
     *     are none.
     */
    public Set<ExtensionInfo> getAllMutableExtensionsByExtendedType(final String fullName) {
      HashSet<ExtensionInfo> extensions = new HashSet<ExtensionInfo>();
      for (DescriptorIntPair pair : mutableExtensionsByNumber.keySet()) {
        if (pair.descriptor.getFullName().equals(fullName)) {
          extensions.add(mutableExtensionsByNumber.get(pair));
        }
      }
      return extensions;
    }
  
    /**
     * Find all extensions for immutable APIs by fully-qualified name of
     * extended class. Note that this method is more computationally expensive
     * than getting a single extension by name or number.
     *
     * @return Information about the extensions found, or {@code null} if there
     *     are none.
     */
    public Set<ExtensionInfo> getAllImmutableExtensionsByExtendedType(final String fullName) {
      HashSet<ExtensionInfo> extensions = new HashSet<ExtensionInfo>();
      for (DescriptorIntPair pair : immutableExtensionsByNumber.keySet()) {
        if (pair.descriptor.getFullName().equals(fullName)) {
          extensions.add(immutableExtensionsByNumber.get(pair));
        }
      }
      return extensions;
    }
  
    /** Add an extension from a generated file to the registry. */
    public void add(final Extension<?, ?> extension) {
      if (extension.getExtensionType() != Extension.ExtensionType.IMMUTABLE &&
          extension.getExtensionType() != Extension.ExtensionType.MUTABLE) {
        // do not support other extension types. ignore
        return;
      }
      add(newExtensionInfo(extension), extension.getExtensionType());
    }
  
    /** Add an extension from a generated file to the registry. */
    public void add(final GeneratedMessage.GeneratedExtension<?, ?> extension) {
      add((Extension<?, ?>) extension);
    }
  
    static ExtensionInfo newExtensionInfo(final Extension<?, ?> extension) {
      if (extension.getDescriptor().getJavaType() ==
          FieldDescriptor.JavaType.MESSAGE) {
        if (extension.getMessageDefaultInstance() == null) {
          throw new IllegalStateException(
              "Registered message-type extension had null default instance: " +
                  extension.getDescriptor().getFullName());
        }
        return new ExtensionInfo(extension.getDescriptor(),
            (Message) extension.getMessageDefaultInstance());
      } else {
        return new ExtensionInfo(extension.getDescriptor(), null);
      }
    }
  
    /** Add a non-message-type extension to the registry by descriptor. */
    public void add(final FieldDescriptor type) {
      if (type.getJavaType() == FieldDescriptor.JavaType.MESSAGE) {
        throw new IllegalArgumentException(
          "ExtensionRegistry.add() must be provided a default instance when " +
          "adding an embedded message extension.");
      }
      ExtensionInfo info = new ExtensionInfo(type, null);
      add(info, Extension.ExtensionType.IMMUTABLE);
      add(info, Extension.ExtensionType.MUTABLE);
    }
  
    /** Add a message-type extension to the registry by descriptor. */
    public void add(final FieldDescriptor type, final Message defaultInstance) {
      if (type.getJavaType() != FieldDescriptor.JavaType.MESSAGE) {
        throw new IllegalArgumentException(
          "ExtensionRegistry.add() provided a default instance for a " +
          "non-message extension.");
      }
        add(new ExtensionInfo(type, defaultInstance),
            Extension.ExtensionType.IMMUTABLE);
    }
  
    // =================================================================
    // Private stuff.
  
    private ExtensionRegistry() {
      this.immutableExtensionsByName = new HashMap<String, ExtensionInfo>();
      this.mutableExtensionsByName = new HashMap<String, ExtensionInfo>();
      this.immutableExtensionsByNumber =
          new HashMap<DescriptorIntPair, ExtensionInfo>();
      this.mutableExtensionsByNumber =
          new HashMap<DescriptorIntPair, ExtensionInfo>();
    }
  
    private ExtensionRegistry(ExtensionRegistry other) {
      super(other);
      this.immutableExtensionsByName =
          Collections.unmodifiableMap(other.immutableExtensionsByName);
      this.mutableExtensionsByName =
          Collections.unmodifiableMap(other.mutableExtensionsByName);
      this.immutableExtensionsByNumber =
          Collections.unmodifiableMap(other.immutableExtensionsByNumber);
      this.mutableExtensionsByNumber =
              Collections.unmodifiableMap(other.mutableExtensionsByNumber);
    }
  
    private final Map<String, ExtensionInfo> immutableExtensionsByName;
    private final Map<String, ExtensionInfo> mutableExtensionsByName;
    private final Map<DescriptorIntPair, ExtensionInfo> immutableExtensionsByNumber;
    private final Map<DescriptorIntPair, ExtensionInfo> mutableExtensionsByNumber;
  
    ExtensionRegistry(boolean empty) {
      super(EMPTY_REGISTRY_LITE);
      this.immutableExtensionsByName =
          Collections.<String, ExtensionInfo>emptyMap();
      this.mutableExtensionsByName =
          Collections.<String, ExtensionInfo>emptyMap();
      this.immutableExtensionsByNumber =
          Collections.<DescriptorIntPair, ExtensionInfo>emptyMap();
      this.mutableExtensionsByNumber =
              Collections.<DescriptorIntPair, ExtensionInfo>emptyMap();
    }
    static final ExtensionRegistry EMPTY_REGISTRY = new ExtensionRegistry(true);
  
    private void add(
        final ExtensionInfo extension,
        final Extension.ExtensionType extensionType) {
      if (!extension.descriptor.isExtension()) {
        throw new IllegalArgumentException(
            "ExtensionRegistry.add() was given a FieldDescriptor for a regular " +
                "(non-extension) field.");
      }
  
      Map<String, ExtensionInfo> extensionsByName;
      Map<DescriptorIntPair, ExtensionInfo> extensionsByNumber;
      switch (extensionType) {
        case IMMUTABLE:
          extensionsByName = immutableExtensionsByName;
          extensionsByNumber = immutableExtensionsByNumber;
          break;
        case MUTABLE:
          extensionsByName = mutableExtensionsByName;
          extensionsByNumber = mutableExtensionsByNumber;
          break;
        default:
          // Ignore the unknown supported type.
          return;
      }
  
      extensionsByName.put(extension.descriptor.getFullName(), extension);
      extensionsByNumber.put(
        new DescriptorIntPair(extension.descriptor.getContainingType(),
                              extension.descriptor.getNumber()),
        extension);
  
      final FieldDescriptor field = extension.descriptor;
      if (field.getContainingType().getOptions().getMessageSetWireFormat() &&
          field.getType() == FieldDescriptor.Type.MESSAGE &&
          field.isOptional() &&
          field.getExtensionScope() == field.getMessageType()) {
        // This is an extension of a MessageSet type defined within the extension
        // type's own scope.  For backwards-compatibility, allow it to be looked
        // up by type name.
        extensionsByName.put(field.getMessageType().getFullName(), extension);
      }
    }
  
    /** A (GenericDescriptor, int) pair, used as a map key. */
    private static final class DescriptorIntPair {
      private final Descriptor descriptor;
      private final int number;
  
      DescriptorIntPair(final Descriptor descriptor, final int number) {
        this.descriptor = descriptor;
        this.number = number;
      }
  
      @Override
      public int hashCode() {
        return descriptor.hashCode() * ((1 << 16) - 1) + number;
      }
      @Override
      public boolean equals(final Object obj) {
        if (!(obj instanceof DescriptorIntPair)) {
          return false;
        }
        final DescriptorIntPair other = (DescriptorIntPair)obj;
        return descriptor == other.descriptor && number == other.number;
      }
    }
  }
  